1. Technical Field
The present invention relates to an endoscopic apparatus.
2. Related Art
An endoscopic device that observes tissues in the body cavity is widely known. Generally, the endoscopic device is configured to irradiate white light (irradiation light) emitted from a white light source such as a xenon lamp onto a subject area to be observed in the body cavity through a light guide and receive the image based on the reflected light from the subject area to be observed by an image pickup device to create an observation image.
Recently, an endoscopic device having observation modes using special light such as narrow band observation that irradiates narrow band light having a specific wavelength band onto a body tissue to observe the blood capillary or a micro pattern of a superficial portion of the mucous membrane or fluorescent observation by auto fluorescence or medicine fluorescence is also used. As the special light, a mixture of light from a white light source such as a xenon lamp and narrow band light from a semiconductor light source such as a laser diode is known (JP-A-2009-201940).
According to the method disclosed in JP-A-2009-201940, since the xenon lamp is used as the white light source, it is difficult to minutely control an emitted light intensity ratio of the white light and the narrow band light. Therefore, instead of the xenon lamp as the white light source, a light source configured by combining a light emitting diode (LED) having long life span and low output variation and a fluorescent may be used. As described above, when two semiconductor light sources are used as the light sources for the special light observation, the output of the semiconductor light sources can be minutely controlled, so that the wavelength balance (emitted light intensity ratio) may be precisely set.
However, it is not easy to modulate the intensity of the light sources while maintaining the wavelength balance of the two semiconductor light sources at a high precision. Specifically, when using a light source, such as an LED, that has a region in which the characteristic of the emitted light intensity with respect to an input current value is nonlinear, it is required to control in consideration of the nonlinearity.